The present invention relates to an apparatus for reducing the volume of various solid waste materials discharged from homes, factories, nuclear power plants, for example, to produce compacted solid masses for landfill or storage, to such an apparatus further comprising its accessory facilities and also to a method for cleaning said apparatus.
Various solid waste materials are discharged from homes, factories, power plants, and other facilities of today. For example, solid wastes such as pieces of plastics, metal, glass, and other materials are discharged from homes and factories, and radioactive wastes such as rags, polyethylene sheets, paper, concrete pieces, steel members, high-performance filters, heat insulation are discharge from nuclear power plants. The aforesaid solid wastes discharged from homes and factories are processed in different ways, which raise their own problems. For example, the discharged pieces of plastics are burned in incinerators. However, the incinerators tend to be melted by heat generated by burning of plastics, clogged by the molten plastics and damaged by local overheating. Furthermore, the incinerators produce harmful gases such as chlorine and dioxin. Landfill of polystyrene foam pieces, polyethylene sheets, plastics bags is disadvantageous in that since these materials are bulky, the cost of transportation thereof is high, and they tend to be exposed onto the landfill surface after buried and then scattered due to winds, resulting in environmental pollution. Various methods have been proposed to recover and reuse waste plastics for effective exploitation of resources. However, since urban trash includes a wide variety of materials, it is more costly to classify the different trash materials than to recover the waste plastics.
It has been proposed in Japanese Patent Publication No. 57-11273 to produce large solid masses containing inorganic particles fixed together with a melt of thermoplastic waste materials by adding a granular or particulate inorganic material such as sand, crushed stone, or ash to the thermoplastic waste materials under heat. This process is however not suitable to granulate metals, fabric pieces and the like, and hence is required to be effected after the metals, fabrics and the like have been separated from the other materials.
The wastes contaminated by a radioactive material in nuclear power plants are normally packed in polyvinyl bags which are placed in drum cans for storage, sometimes after having been classified into combustible and noncombustible materials.
Waste materials such as high-performance filters composed of a wood material, a filter aid (inorganic), a metal plate and the like which are joined together are required to be disassembled into individual parts which should then be sorted. This process is complicated and gives the workers a greater chance to get exposed to radiation.
The drum cans are stored in storage houses. Since the available storage spaces in the storage houses are becoming smaller than expected these days, the combustible radioactive wastes are burned and the produced ash is stored in drum cans or mixed with cement and solidified as stable solid masses. The burning process is used for processing the bulky materials such as polyethylene sheets, polyvinyl bags, rags and paper wastes, and hence is capable of reducing the volumes of these waste materials. For this reason, the burning process is widely employed to process the waste materials discharged from nuclear power plants, facilities using radioisotopes, and other similar facilities.
However, when a large quantity of plastic materials are burned in an incinerator, the incinerator is liable to get damaged, and the incinerator system is required to be equipped with an exhaust gas processing apparatus which itself produces a secondary waste material. In addition, the cost of installation of said apparatus is high.
Another process of treating radioactive solid waste materials is to employ a press for compacting the wastes into smaller volumes. There is developed a high-pressure compacting apparatus for compacting waste materials under a pressure ranging from 1000 to 3000 kg/cm.sup.2. According to this compacting process, polyethylene sheets, polyvinyl bags, paper wastes, rags and similar waste materials can be compacted into masses free of free spaces or air pockets trapped therein. Although the compacting process is one of effective methods, produced compacted masses are combinations of heterogeneous materials that are not desired for a long-term storage.